The invention relates generally to the field of information storage and more particularly relates to hard disk drives.
U.S. Pat. No. 5,831,888 entitled xe2x80x9cAutomatic Gain Control Circuitxe2x80x9d and assigned to Texas Instruments Incorporated, the assignee of the present invention, sets forth generally the description of disk storage for information. Hard disk drives (HDD) are one type of disk storage that is particularly used in personal computers today. The HDD device generally includes a magnetic storage media, such as rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servocontroller, a memory and control circuitry to control the operation of the HDD and to properly interface the HDD to a host or system bus. The following U.S. Patents describe various aspects of HDD devices:
Prior art FIG. 1 illustrates a disk/head assembly 12 and a preamplifier 14. The preamplifier 14 handles both read functions and write functions. Not illustrated in FIG. 1, for clarity, is the Read Write (RW) Head. The unshown RW head works through magnetic media and it contains both functions, read and write, with a different portion of the head performing each function. The write function portion of the MR head is inductive and the read function portion of the head acts as a magnetic resistive (MR) element. A write occurs through an inductive element to the magnetic media disk assembly 12 and a read occurs by sensing the magnetic shifts in the disk assembly 12 by using the resistive read element. As explained below, undesirable magnetic or capacitive coupling often occurs between the writer element in the RW head and the reader element because of their close proximity to each other.
Prior art FIG. 2 depicts a circuit representation the write channel 16 and the read channel 18 of the preamplifier 14 of FIG. 1. The writer 16 is connected to an inductor 20. During a write, the preamplifier 14, through the write channel 18, drives a current 22 through the inductor 20 of the RW head. In close proximity to the inductor 20, is a resistive element 24 on the read channel 18. The value of the resistive element 24 is a function of the magnetic field. Because of the physical closeness of the inductor 20 and the resistive element 24 of the RW head, magnetic or capacitive coupling naturally occurs. This undesirable coupling is represented by the capacitor shown at reference numeral 21. The concern is that this coupling will change the resistive value in the reader portion of the RW head.
In a personal computer during a typical operation, a read and a write to the RW head do not occur at the same time. Only one function at a time is performed; both do not occur simultaneously. In normal read and write operations, a bias current 26 is maintained through the resistive reader element 24 to keep it ready for the read mode. The RW head is very sensitive to current, particularly in the wrong direction. So, typically a bias current 26 is provided to offset any undesirable effects from magnetic coupling.
At the manufacturer, when formatting the disk/head assembly 12, all of the RW heads (1 to 12 at present) are written to at the same time. This is known in the industry as the servo track write mode operation or the servo bank write mode operation. In servo bank write mode, when the disk/head assembly 12 is formatted, all RW heads are written to at the same time to write the servo track wedges on the disks. However, unlike the bias current which is maintained on the read portion of the RW head during a normal write operation, the bias current for all the read channel is not turned on during servo bank write mode as the added power dissipation for having the full RW bias on for all heads may exceed the thermal requirements for the preamplifier.
Prior art FIG. 3 depicts the voltage waveforms of the RW head during servo track mode. The writer voltage is Vw. The reader voltage is Vrmr. If no magnetic coupling existed, when Vw rises, Vrmr would maintain its zero value. However, magnetic (or capacitive) coupling, spikes a voltage on the reader portion of the RW head, which in turn spikes a current. This becomes more of a problem with a new generation of heads because if they have a negative going current, it can greatly upset the magnetic properties of the element and cause it to not read back information from the disk assembly 12 properly. A GMR (Giant Magneto Resistance) RW head is typical of such a newelement having these problems. These heads are extremely sensitive to the negative going currents (voltages). These spikes damage the head, which results in less amplitude output from the head and asymmetric response that yield data bit errors.
It is accordingly an object of this invention to prevent the GMR element in a RW head from becoming upset from its natural state. The negative going current spikes on the reader portion of the head must be eliminated during servo bank write mode when all heads are written to simultaneously.
Other objects and advantages of the invention herein will be apparent to those of ordinary skill in the art having the benefit of the description herein.
The invention solves the problem of current spikes occurring in the reader portion of a Read Write head of a HDD during servo bank write mode at the HDD manufacturer. During this process when the manufacturer formats the disk assembly, all heads are simultaneously written to. The undesirable current spikes in the read heads are eliminated by providing a relatively small bias current to all read heads during the servo bank write mode. This raises the dc bias level on the reader portion of the RW head to eliminate the negative spikes generated through capacitive or magnetic coupling. The voltage Vrmr appearing on the reader head is prevented from going below zero volts. Thus, the MR element is not upset from its natural state and bit error rates are reduced.